Oxazolyl-substituted thiadiazolidinediones

ABSTRACT

Thiadiazolidinediones substituted by a 5-substituted-1,2-oxazol-3-yl moiety, useful for controlling the growth of unwanted plants.

DESCRIPTION OF THE INVENTION

It has been found that the growth of certain plants is adversely affected by compounds of the formula: ##STR1## wherein one of R¹ and R² is a moiety ##STR2## and the other is alkyl, (mono- or polyhalo)alkyl or alkoxy of from one to three carbon atoms, cycloalkyl of from three to six carbon atoms, or alkenyl of from three to five carbon atoms, R³ containing from three to five carbon atoms and being one of alkyl, alkenyl, alkynyl, alkoxyalkyl, alkylthioalkyl, alkylsulfinylalkyl, alkylsulfonylalkyl, cycloalkyl, alkylcycloalkyl, and (mono- and polyhalo)alkyl.

In these compounds, each alkyl, alkoxy, alkenyl and alkynyl moiety suitably is either straight-chain or branched-chain in configuration. The term "halo"--i.e., halogen--designates one of chlorine, bromine and fluorine. Preferred alkylthioalkyl, alkylsulfinylalkyl and alkylsulfonylalkyl moieties are those of the formula: ##STR3## wherein n is zero, one or two.

Because of their biological characteristics, the compounds of the subclass of Formula I wherein R¹ is ##STR4## are to be preferred, R³ preferably being tertiary-butyl.

Compounds of Formula I can be prepared by treating the appropriate R¹, R² -urea (Formula II, following) with (chlorothio)formyl chloride in the presence of an inert solvent, and in the presence of a tertiary nitrogen base as hydrogen chloride acceptor. The reaction proceeds according to the equation: ##STR5##

Treatment of the urea with (chlorothio)formyl chloride is conveniently conducted by adding the chloride to a stirred solution of the urea in a solvent at about room temperature, chilling the resulting mixture to about 0° C., slowly adding the amine thereto, then warming and stirring the mixture until the reaction is complete. In some cases, it may be found to be desirable to use a disulfide ##STR6## wherein R is a hydrocarbon moiety) or ester ##STR7## instead of (chlorothio)formyl chloride. In such cases, the intermediate product (the starred hydrogen in Formula II is replaced by the moiety ##STR8## respectively) is cyclized by heat, in the case of the ester the cyclization being catalyzed by a base.

(Chlorothio)formyl chloride, the disulfides and esters are all known compounds. Workup of the reaction mixture, isolation of the product and its purification are effected by conventional techniques, as illustrated in the examples, hereinafter.

Most of the oxazolyurea precursors (Formula II) are known compounds: U.S. Pat. No. 4,062,861. Those wherein R³ represents a moiety ##STR9## can be prepared by methods shown in that patent, the precursor amine being prepared from the nitrile, according to the procedure shown in Examples 1 and 2, the nitrile being prepared from methyl 2-methyl-2-methylthiopropionate, by adding a mixture of that ester and acetonitrile to sodium hydride in a suitable solvent, such as tetrahydrofuran, at a moderately elevated temperature--for example, 60°-80° C. The ester can be prepared from methyl 2-bromo-2-methylpropionate (C. C. Price and E. C. Coyner, J. Am. Chem. Soc., (1940) 62, 1306-7) by the procedure shown in U.S. Pat. No. 3,994,997 for the preparation of the ethyl ester.

The oxazolylamine precursor wherein R³ =tertiary-butyl is the subject of British Pat. No. 2,014,992. The others can be prepared by the procedures described in that patent. Preparation of particular species of the precursor amines are shown in the examples, hereinafter.

Those compounds of Formula I wherein R³ is the moiety ##STR10## wherein n is one or two, can be prepared by conventional oxidation of the corresponding compounds of Formula I wherein n is zero. The oxidations can be effected by using such oxidizing reagents as hydrogen peroxide/acetic acid, peracids (for example meta-chloroperbenzoic acid), sodium metaperiodate, chromic acid/acetic acid, nitric acid, or potassium permanganate/acetic acid (or acetone), as described in "Methoden der Organischen Chemie," (Houben-Weyl), Schewfel-, selen-, und TellurVerbindungen, vol. IX, pp. 207 & 208, Thieme Verlag, Stuttgart, Germany (1955).

The preparation, isolation and testing of three typical individual species of the compounds of Formula I are described in the example, following. The class of compounds is further illustrated and exemplified by the following further individual species, all of which are specifically contemplated in this invention. In the interest of brevity, in the identification of these species, the class of compounds defined in Formula I will be considered as being made up of two subclasses: Subclass A, wherein R¹ is the oxazolyl moiety, and Subclass B, wherein R² is the oxazolyl moiety. The following are the species in question:

    ______________________________________                                         Species                                                                        No.     R.sup.2     R.sup.3                                                    ______________________________________                                         Subclass A:                                                                    1       methoxy     tertiary-butyl                                                                 ((CH.sub.3).sub.3 C)                                       2       cyclopropyl tertiary-butyl                                             3       isopropyl   tertiary-butyl                                             4       methyl      1,1-dimethyl-2-propyn-1-yl                                                     (HCCC(CH.sub.3).sub.2)                                     5       methyl      1-methylcyclopropyl                                                             ##STR11##                                                 6       methyl      2-methoxy-1,1-di-methyl-                                                       ethyl                                                                          (CH.sub.3OCH.sub.2C(CH.sub.3).sub.2)                       7       methyl      1-methyl-1-methylthio-                                                         ethyl(CH.sub.3SC(CH.sub.3).sub.2                           8       methyl      1-methyl-1-methylsulfenyl-                                                     ethyl(CH.sub.3S(O)C(CH.sub.3).sub.2)                       9       methyl      1-methyl-1-methylsulfonyl-                                                     ethyl(CH.sub.3S(O).sub.2C(CH.sub.3).sub.2)                 Subclass B:                                                                    10      methyl      1,1-dimethyl-2-propyn-1-yl                                 11      methoxy     tertiary-butyl                                             ______________________________________                                    

The preparation, isolation and physical properties of typical individual species of the compounds of Formula I, in particular instances, are described in the following examples. In each case, the identity of the product, and each of any intermediate involved, was confirmed by appropriate chemical and spectral analyses.

EXAMPLE 1 -4-Methyl-2-((5-tertiary-butyl)-1,2-oxazol-3-yl)-1,2,4-thiadiazolidine-3,5-dione (1); 2-Methyl-4-((5-tertiary-butyl)-1,2-oxazol-3-yl)-1,2,4-thiadiazolidine-3,5-dione (2)

A solution of 41.5 g of hydroxylamine hydrochloride in 136 ml of water was added drop-by-drop over a 10-minute period to a stirred, refluxing mixture of 56.1 g of pivaloylacetonitrile (British patent 2,014,992), 700 ml of water and 525 ml of ethanol. The mixture was held under those conditions for 7 hours, the pH of the mixture being periodically adjusted to 6.5 by the addition of either hydrogen chloride or aqueous sodium hydroxide solution, as required. Then the solvent ethanol was evaporated in a rotary evaporator, the residual liquid was dried (MgSO₄), and placed in 200 ml of hexane and chilled. Filtration and fractional crystallization of the solid gave 3-amino-5-(tertiary-butyl)-1,2-oxazole (1A), a yellow solid, m.p.: 107°-109° C. A second fraction was 5-amino-3-(tertiary-butyl)-1,2-oxazole (1B), a solid, m.p.: 89°-90° C.

1A was converted to 1-methyl-3-(5-(tertiary-butyl)-1,2-oxazol-3-yl)urea (1C) by the method and procedures disclosed in U.S. Pat. No. 4,062,861.

40.8 g of (chlorothio)formyl chloride was added to a stirred solution of 50.0 g of 1C in 800 ml of methylene chloride at room temperature. The resulting solution was cooled and held at 10°-15° C. while 80.6 g of ethyldiisopropylamine was added drop-by-drop in two hours. The resulting mixture was stirred for 16 hours at room temperature, then mixed with water and extracted with methylene chloride. The extract was dried (MgSO₄), the solvent was evaporated, and the residue was adsorbed on silica gel and eluted with a 1:4:20 v:v:v mixture of tetrahydrofuran, ethyl acetate and hexane. The first fraction that was obtained consisted of the starting urea. Upon recrystallization from ether-hexane, the second fraction gave 1, an off-white solid, m.p.: 113°-114° C. The third fraction was 2, a light yellow solid, m.p.: 114°-115° C. The melting point of a mixture of 1 and 2 was depressed (92°-95° C.).

EXAMPLE 2 4-Methyl-((5-(1,1-dimethyl-2-methoxyethyl)-1,2-oxazol-3-yl)-1,2,4-thiadiazolidine-3,5-dione (3)

219 g of chloropivaloyl chloride was added drop-by-drop to a chilled (0°-5° C.), stirred solution of 141.4 g of triethylamine in 320 g of anhydrous methanol. The resulting mixture was warmed to room temperature in one hour, and most of the methanol was evaporated under reduced pressure. The residue was mixed with water and extracted with ether. The extract was dried (MgSO₄), and the solvent was evaporated. The residue was distilled to give methyl 3-chloro-2,2-dimethylpropionate (3A), b.p.: 40°-50° C. (14 Torr.).

A solution of 168.3 g of 3A in 76 g of acetonitrile and 118 ml of tetrahydrofuran was added drop-by-drop over a one-hour period to a stirred, refluxing mixture of 42.2 g of sodium hydride and 766 ml of tetrahydrofuran. The resulting mixture was stirred and refluxed for 18 hours, then part of the solvent was evaporated. The residue was added to 1 liter of ice water, and the resulting mixture was acidified with hydrochloric acid and extracted with ether. The extract was dried (MgSO₄) and distilled to give (1-(methoxymethyl)-1-methylethyl)carbonyl)acetonitrile 3B, as a colorless liquid, b.p.: 86°-90° C. (0.2 Torr.).

A solution of 58.5 g of hydroxylamine hydrochloride in 88 ml of water was added drop-by-drop over a 10-minute period to a stirred, refluxing solution of 100.9 g of 3B and 33.7 g of sodium hydroxide in 950 ml of water and 740 ml of ethanol. The mixture was stirred and refluxed for 18 hours, then the ethanol was evaporated in a rotary evaporator. The aqueous residue was cooled and filtered. The solid was chromatographed over silica gel, using a 2:15:33 v:v:v mixture of tetrahydrofuran ethyl acetate and hexane as eluent, to give 3-amino-5-(1-(methoxymethyl)-1-methylethyl)-1,2-oxazole (3C), as a cream-colored solid, m.p.: 61°-64° C.

A solution of 1.0 g of 3C and 1.0 g of methyl isocyanate in 15 ml of anhydrous ether was held at room temperature for 3 days. Then the solvent was evaporated and the residue was crystallized from hexane to give 1-methyl-3-(5-(1,1-dimethyl-2-methoxyethyl)-1,2-oxazol-3-yl)urea (3D), as a colorless solid, m.p.: 113°-115° C.

10.0 g of 3D was treated with (chlorothio)formyl chloride and ethyldiisopropylamine by the procedure described in Example 1, to give 3, as a light yellow solid, m.p.: 65°-67° C.

Compounds of Formula I have been found to adversely affect the growth of plants, many of which are commonly considered as weeds, and therefore to be useful for controlling the growth of such unwanted plants. Compounds of Formula I have been found to have selectivity with respect to some crop plants--i.e., they control weeds at dosages at which they do not significantly harm the crop plants. Compounds of Formula I appear to be effective when applied preemergence or preplant incorporated (applied to the soil before the seeds have sprouted) or when applied postemergence (applied to the foliage of the growing plant). Some appear to be somewhat more effective when applied preemergence than when applied postemergence.

Accordingly, the invention includes a method of combatting unwanted plants which comprises applying to the locus an effective amount of a compound of Formula I. In the cases where it is desired to control weeds in crop plantings, it is of course preferable to employ the lowest dosage that will control the weeds, for this will minimize any possible deleterious effect of the compound upon the crop plants. For application, the compound generally is applied most effectively by formulating it with a suitable inert carrier or surface-active agent, or both. The invention, therefore, also includes compositions suitable for combatting unwanted plants, such compositions comprising an inert carrier or surface-active agent, or both, and as active ingredient at least one compound of Formula I.

The term "carrier" as used herein means an inert solid or fluid material, which may be inorganic or organic and of synthetic or natural origin, with which the active compound is mixed or formulated to facilitate its application to the plant, seed, soil or other object to be treated, or its storage, transport and/or handling. Any of the materials customarily employed in formulating pesticides, herbicides, or fungicides, are suitable.

Suitable solid carriers are natural and synthetic clays and silicates, for example, natural silicas such as diatomaceous earths; magnesium silicates, for example, talcs; magnesium aluminum silicates, for example, attapulgites and vermiculites; aluminum silicates, for example, kaolinites, montmorillonites and micas; calcium carbonate; calcium sulfate; synthetic hydrated silicon oxides and synthetic calcium or aluminum silicates; elements such as, for example, carbon and sulfur; natural and synthetic resins such as, for example, coumarone resins, polyvinyl chloride and styrene polymers and copolymers; bitumen; waxes such as, for example, beeswax, paraffin wax, and chlorinated mineral waxes; solid fertilizers, for example, superphosphates; and ground, naturally-occurring, fibrous materials, such as ground corncobs.

Examples of suitable fluid carriers are water, alcohols such as, for example, isopropyl alcohol, ketones such as, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ethers such as, for example, cellosolves; aromatic hydrocarbons such as, for example, benzene, toluene and xylene; petroleum fractions such as, for example, kerosene, light mineral oils; chlorinated hydrocarbons such as, for example, carbon tetrachloride, perchloroethylene, trichloroethane, including liquefied, normally vaporous, gaseous compounds. Mixtures of different liquids are often suitable.

The surface-active agent may be an emulsifying agent or a dispersing agent or a wetting agent; it may be nonionic or ionic. Any of the surface-active agents usually applied in formulating herbicides or insecticides may be used. Examples of suitable surface-active agents are the sodium or calcium salts of polyacrylic acids and lignin sulfonic acids; the condensation products of fatty acids or aliphatic amines or amides containing at least 12 carbon atoms in the molecule with ethylene oxide and/or propylene oxide; fatty acid esters of glycerol, sorbitan, sucrose or pentaerythritol; condensates of these with ethylene oxide and/or propylene oxide; condensation products of fatty alcohols or alkyl phenols, for example, p-octylphenol or p-octylcresol, with ethylene oxide and/or propylene oxide; sulfates or sulfonates of these condensation products, alkali or alkaline earth metal salts, preferably sodium salts, or sulfuric or sulfonic acid esters containing at least 10 carbon atoms in the molecule, for example, sodium lauryl sulfate, sodium secondary alkyl sulfates, sodium salts of sulfonated castor oil, and sodium alkyl-aryl sulfonates such as sodium dodecylbenzene sulfonate; and polymers of ethylene oxide and copolymers of ethylene oxide and propylene oxides.

The compositions of the invention may be prepared as wettable powders, dusts, granules, solutions, emulsifiable concentrates, emulsions, suspension concentrates and aerosols. Wettable powders are usually compounded to contain 25, 50 or 75% by weight of the active compound and usually contain, in addition to the solid carrier, 3-10% by weight of a dispersing agent, 15% of a surface-active agent and, where necessary, 0-10% by weight of stabilizer(s) and/or other additives such as penetrants or stickers. Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant or surface-active agent, and are diluted in the field with further solid carrier to give a composition usually containing 0.5-10% by weight of the active compound. Granules are usually prepared to have a size between 10 and 100 BS mesh (1.676-0.152 mm), and may be manufactured by agglomeration or impregnation techniques. Generally, granules will contain 0.5-25% by weight of the active compound, 0-1% by weight of additives such as stabilizers, slow release modifiers and binding agents. Emulsifiable concentrates usually contain, in addition to the solvent and, when necessary, cosolvent, 10-50% weight per volume of the active compound, 2-20% weight per volume emulsifiers and 0-20% weight per volume of appropriate additives such as stabilizers, penetrants and corrosion inhibitors. Suspension concentrates are compounded so as to obtain a stable, non-sedimenting, flowable product and usually contain 10-75% weight of the active compound, 0.5-5% weight of dispersing agents, 1-5% of surface-active agent, 0.1-10% weight of suspending agents, such as defoamers, corrosion inhibitors, stabilizers, penetrants and stickers, and as carrier, water or an organic liquid in which the active compound is substantially insoluble; certain organic solids or inorganic salts may be dissolved in the carrier to assist in preventing sedimentation or as antifreeze agents for water.

Aqueous dispersions and emulsions, for example, compositions obtained by diluting a wettable powder or a concentrate according to the invention with water, also lie within the scope of the present invention. The said emulsions may be of the water-in-oil or of the oil-in-water type, and may have a thick, mayonnaise-like consistency.

The compositions of the invention may also contain other ingredients, for example, other compounds possessing pesticidal, especially insecticidal, acaricidal, herbicidal or fungicidal properties, as are appropriate to the intended purpose.

Protection of a locus or area from undesirable plants is effected by applying a compound of Formula I, ordinarily in a composition of one of the aforementioned types, to soil in which the seeds of the unwanted plants are present, or to the foliage of the unwanted plants. The active compound, of course, is applied in an amount sufficient to exert the desired action.

The amount of the compound of the invention to be used in combatting undesired plants will naturally depend on the condition of the plants, the degree of activity desired, the formulation used, the mode of application, the climate, the season of the year, and other variables. Recommendations as to precise amounts are, therefore, not possible. In general, however, application to the locus to be protected of from 0.1 to 10.0 kg per hectare of the compound of Formula I will be satisfactory.

Examples of Activity with Respect to Plants

In the following examples, the species of plants that were tested were:

Barnyardgrass (watergrass)--Enchinochloa crus-galli

Large crabgrass--Digitaria sanguinalis

Downy brome--Bromus tectorum

Yellow foxtail--Setaria lutescens

Redroot pigweed--Amaranthus retroflexus

Sicklepod--Cassia obtusifolia

Velvetleaf--Abutilon Theophrasti

Garden cress--Lepidium sativum

Johnsongrass--Sorghum halepense

Test Procedures

The preemergence (soil) herbicidal activity of the compounds was evaluated by planting seeds of barnyardgrass, garden cress, downy brome, velvetleaf, yellow foxtail, and sicklepod in test tubes, nominally measuring 25×200 millimeters, filled about three-quarters full of untreated soil, in each case covered on top with about 2.5 cubic centimeters of soil treated with a certain amount of the test compound. The treated soil applied to the tubes containing the barnyardgrass and cress seeds contained one milligram of the test compound per tube, and contained 0.1 milligram of the test compound per each tube containing the seeds of the other plants. The dosages were approximately 20 and 2.0 pounds of test compound per acre, respectively. The seeds were planted on top of the treated soil and covered with about 1.5 cubic centimeters of untreated soil. The planted soil was held under controlled conditions of temperature, moisture, and light for 9 to 10 days. The amounts of germination and growth in each tube were evaluated on a 0 to 9 scale, the numeric ratings having the following meanings:

    ______________________________________                                         Rating  Meaning                                                                ______________________________________                                         9       No living tissue                                                       8       Plant severely damaged and expected to die                             7       Plant badly damaged, but expected to live                              6       Moderate damage, but complete recovery expected                        5       Intermediate damage (probably unacceptable for                                 crop plants)                                                           3-4     Observable damage                                                      1-2     Plant slightly affected, possibly by the chemical,                             possibly due to biological variability                                 0       No visible effect                                                      ______________________________________                                    

The postemergence (foliar) herbicidal activity of compounds of the invention was evaluated by spraying 10-day-old large downy brome plants in some cases, 6-day-old Johnsongrass plants in other cases, 9-day-old velvetleaf plants, 9-day-old yellow foxtail plants and 9-day-old sicklepod plants to runoff with a liquid formulation of the test compound. The crabgrass and pigweed plants were sprayed with 2.4 milliliters of a 0.25% solution (about ten pounds of the test compound per acre), and other plants were sprayed with 2.4 milliliters of a 0.025% solution (about one pound of the test compound per acre). The sprayed plants were held under controlled conditions of temperature, moisture and light for 7 to 8 days, and the effect of the test compound was then evaluated visually, the results being rated on the 0 to 9 scale described above.

Results of the preemergence and postemergence herbicidal activity tests are set forth in Table I.

                                      TABLE I                                      __________________________________________________________________________     HERBICIDAL ACTIVITY                                                            Preemergence                        Postemergence                                    Barnyard-                                                                            Garden                                                                              Downy                                                                               Velvet-                                                                             Yellow                                                                             Sickle-                                                                             Crab-                                                                              Pig-                                                                              Johnson-                                                                            Velvet-                                                                             Yellow                                                                              Sickle-              Compound                                                                             grass Cress                                                                               Brome                                                                               leaf Foxtail                                                                            pod  grass                                                                              weed                                                                              grass                                                                               leaf Foxtail                                                                             pod                  __________________________________________________________________________     1     9     9    9    9    9   9    9   9  2    9    9    9                    2     9     9    8    8    8   8    9   9  5    6    2    9                    3     8     9    3    8    5   8    4   8  2    3    2    3                    __________________________________________________________________________

EXAMPLES OF SELECTIVITY

In the following examples, the species of plants that were tested were:

Barnyardgrass

Downy brome

Johnsongrass

Wild oats--Avena fatua

Yellow foxtail

Goose grass--Eleusine indica L.

Yellow nutsedge--Cyperus esculentus L.

Cocklebur--Xanthum pennsylvanicum

Morning glory--Ipomoea purpurea L.(Roth)

Wild mustard--Brassica kaber

Redroot pigweed

Sicklepod

Velvetleaf

Corn--Zea mays

Cotton--Gossypium hirsutum

Rice--Oryza sativa

Grain sorghum--Sorghum vulagare

Soybeans--Glycine max

Sugarbeets--Beta vulgaris

Wheat--Triticum aestivum

Test Procedures

The preemergence activity of compounds of Formula I was further determined with respect to certain species of crop plants and common species of weeds, by spraying a formulation of the test compound on soil in small pots in which seeds of the plants had been sown. The results of the tests were evaluated on the basis of the 0-9 scale described with respect to the earlier tests. The results of the tests are reported in Tables II and III.

                  TABLE II                                                         ______________________________________                                         COMPOUND 1                                                                              Rating of Effect at Indicated Dosage (lb/acre)                                 Preemergence                                                          Plant Species                                                                             0.25           0.0625                                               ______________________________________                                         Corn       2              0                                                    Cotton     0              0                                                    Rice       9              7                                                    Grain Sorghum                                                                             7              3                                                    Soybean    9              2                                                    Sugar Beet 9              9                                                    Wheat      9              6                                                    Barnyard Grass                                                                            8              6                                                    Downy Brome                                                                               5              4                                                    Johnsongrass                                                                              8              0                                                    Wild Oats  9              5                                                    Yellow Foxtail                                                                            7              0                                                    Goose Grass                                                                               9              0                                                    Yellow Nutsedge                                                                           --             --                                                   Cocklebur  9              9                                                    Morning Glory                                                                             9              9                                                    Mustard    9              9                                                    Pigweed    9              9                                                    Sicklepod  9              3                                                    Velvetleaf 9              4                                                    ______________________________________                                    

                  TABLE III                                                        ______________________________________                                         COMPOUND 2                                                                              Rating of Effect at Indicated Dosage (lb/acre)                                 Preemergence                                                          Plant Species                                                                             0.25           0.0625                                               ______________________________________                                         Corn       2              0                                                    Cotton     3              0                                                    Rice       8              0                                                    Grain Sorghum                                                                             7              0                                                    Soybean    8              3                                                    Sugar Beet 9              9                                                    Wheat      9              8                                                    Barnyard Grass                                                                            8              7                                                    Downy Brome                                                                               0              0                                                    Johnsongrass                                                                              9              6                                                    Wild Oats  9              9                                                    Yellow Foxtail                                                                            --             6                                                    Goose grass                                                                               9              9                                                    Yellow Nutsedge                                                                           --             0                                                    Cocklebur  7              9                                                    Morning Glory                                                                             9              0                                                    Mustard    9              9                                                    Pigweed    9              9                                                    Sicklepod  9              9                                                    Velvetleaf 9              9                                                    ______________________________________                                    

In such tests, Compound 3 was found to be inactive with respect to all of the species of plants when applied preemergence at dosages of 0.25 and 0.125 pounds/acre. 

I claim:
 1. A compound of the formula ##STR12## wherein one of R¹ and R² is a moiety ##STR13## and the other is alkyl, (mono- or polyhalo)alkyl, or alkoxy, of from one to three carbon atoms, cycloalkyl of from three to five carbon atoms, or alkenyl of from three to five carbon atoms, R³ containing from three to five carbon atoms and being one of alkyl, alkenyl, alkynyl, alkoxyalkyl, alkylthioalkyl, alkylsulfinylalkyl, alkylsulfonylalkyl, cycloalkyl, alkylcycloalkyl, and (mono- and polyhalo)alkyl.
 2. A compound according to claim 1 wherein R¹ is ##STR14## and R² is alkyl.
 3. A compound according to claim 2 wherein R³ is tertiary-butyl and R² is methyl.
 4. A method for controlling the growth of unwanted plants at a locus which comprises applying to the locus an effective amount of a compound of claim
 1. 5. A method for controlling the growth of unwanted plants at a locus which comprises applying to the locus an effective amount of a compound of claim
 2. 6. A method for controlling the growth of unwanted plants at a locus which comprises applying to the locus an effective amount of the compound of claim
 3. 7. A composition adopted to control unwanted plants which comprises an effective amount of a compound of claim 1 and an inert carrier, a surface-active agent, or both.
 8. A composition of claim 7 wherein R¹ is ##STR15## and R² is alkyl.
 9. A composition according to claim 8 wherein R³ is tertiary-butyl and R² is methyl. 